The wind is one of the oldest sources of power. Valk Windmill is a fine example of how this natural energy source has been effectively harnessed.
You'll have sightseeing choices galore when staying in Leiden. Valk Windmill is a good place to kick off here, but there are plenty of other worthwhile places to enjoy. Duinrell, Katwijk Aan Zee Beach, and Corpus are not far from the wind-driven milling structure and will top off your day nicely.